Fixed Header Style (Scroll Back) Glitch When Scrolling Back to Top?

Site URL: https://www.artestar.com/

Site URL: https://www.artestar.com/

I'm currently using the fixed header with the "scroll back" option in Squarespace 7.1 and am hoping for some help with an issue I'm having:

The "scroll back" header functions fine when scrolling through the pages on my site (top to bottom), but upon scrolling back to the top of the page, the header seems to have a slight glitch. After scrolling to the top from the bottom of the page, the header reappears, but in one quick motion it pushes the top-most section down slightly. Seeing this glitch motion each time I scroll to the top of my site is quite displeasing. 

Has anyone experienced this issue or have any potential solutions?

Many thanks!